F5CAB2 Exam Dumps : BIG-IP Administration Data Plane Concepts (F5CAB2) exam

In BIG-IP high availability (HA) configurations, MAC Masquerade is used to speed up failover by allowing traffic-group-associated Self IPs to retain the same MAC address when moving between devices. This prevents upstream switches and routers from having to relearn ARP entries during a failover event, resulting in near-instant traffic recovery.

By default, MAC masquerade applies one MAC address per traffic group, regardless of how many VLANs the traffic group spans. This can create problems in some network designs because the same MAC address appearing on multiple VLANs may violate network policies or confuse switching infrastructure.

To address this, BIG-IP provides Per-VLAN MAC Masquerade, enabled by the database variable:

`tm.macmasqaddr_per_vlan = true`

When this feature is enabled:

BIG-IP derives a unique MAC address per VLAN

The base MAC address configured on the traffic group remains the first four octets

The last two octets are replaced with the VLAN ID expressed in hexadecimal

The VLAN ID is encoded in network byte order (high byte first, low byte second)

### VLAN ID Conversion:

VLAN ID: 1501 (decimal)

Convert to hexadecimal:

1501₁₀ = 0x05DD

High byte: 05

Low byte: DD

### Resulting MAC Address:

Base MAC: `02:12:34:56:00:00`

Per-VLAN substitution → last two bytes = `05:DD`

Final MAC address:

`02:12:34:56:05:dd`

### Why the Other Options Are Incorrect:

A (01:15) – Incorrect hexadecimal conversion of 1501

B (dd:05) – Byte order reversed (little-endian, not used by BIG-IP)

D (15:01) – Uses decimal values instead of hexadecimal

### Key BIG-IP HA Concept Reinforced:

Per-VLAN MAC Masquerade ensures Layer 2 uniqueness per VLAN while preserving the fast failover benefits of traffic groups, making it the recommended best practice in multi-VLAN HA deployments.

In the BIG-IP system, VLANs are the logical entities that group physical interfaces or trunks together. To modify how a VLAN interacts with an interface, the administrator must navigate to the specific VLAN configuration object.

VLAN List:This section displays all existing VLANs configured on the system.

Interface Association:Within the properties of a specific VLAN (in this case, "external"), there is anInterfacessection. This is where physical ports or trunks are assigned to the VLAN.

Tagging Status:For each associated interface, the administrator can choose betweenTagged(802.1Q) orUntagged.

Untagged:The interface will treat incoming traffic without a VLAN header as part of this VLAN, and outgoing traffic will not have a VLAN tag added. An interface can only be "Untagged" for one VLAN.

Tagged:Allows an interface to carry traffic for multiple VLANs simultaneously by using 802.1Q headers.

In the F5 BIG-IP ecosystem, atrunkis a logical grouping of two or more physical interfaces that the system treats as a single data path. This configuration is based on the Link Aggregation Control Protocol (LACP) or static link aggregation.

Trunks provide two primary benefits to the data plane:

Increased Bandwidth:By aggregating multiple physical interfaces (e.g., combining two 10Gbps interfaces), the aggregate throughput of the logical connection is increased. This allows the BIG-IP to handle higher traffic volumes than a single interface could support.

Link Redundancy:Trunks provide high availability at the physical layer. If one physical interface within the trunk fails or the cable is disconnected, the BIG-IP system automatically redistributes traffic across the remaining active interfaces in the trunk. This prevents a single cable or port failure from causing a network outage.

Why the other options are incorrect:

Option C:While VLAN tags are often usedontrunks, the ability to use tagged VLANs is a property of theVLANconfiguration and 802.1Q tagging, not the trunk itself. A single interface can support tagged VLANs without being part of a trunk.

Option D:Trunks are agnostic to the type of application traffic (such as VoIP) passing through them. They operate at Layer 2 to provide a reliable pipe for any Layer 3+ traffic.